Hello Salima,
Welcome to the Disney Parks Moms Panel with your travel planning question. I am sure you are looking forward to your exciting adventure at Walt Disney World. There is so much to see and do that I know you will have a fantastic time.
When riding an attraction, you can take your backpacks and tote bags on the ride with you, unless your bag is particularly extra large. We always take an average backpack with us into the parks and have never had an attraction that we could not fit it in. However, there are
locker rentals available in each of the theme parks. The only drawback is that they are located at the park entrances, so they are not convenient enough to go back and forth to between rides.
Another tip I often tell my family and friends about is taking a folded up trash bag to place around your backpack or tote on the rides where getting wet is possible. Once you finish the ride, remove the trash bag and shake it out and fold back up for the next use.
I hope this helps in your planning. Have a wonderful time.
~Allison L